The dorsolateral prefrontal (PFC) and posterior parietal cortex (PPC) are known to represent visuospatial information and to be activated by tasks involving the subjects' attention processes. Recent reports have suggested that salient stimuli are encoded first by PPC during bottom-up attention; however, previous experiments have not used tasks driven entirely by bottom-up signals. We developed a behavioral task that orients attention based purely on bottom-up factors and tested the hypothesis that responses to the salient stimuli emerge earlier in PPC than in PFC. Electrophysiological recordings were made in area 46 of PFC and area 7a of PPC which are known to be strongly interconnected. A stimulus array consisting of one target stimulus differing in color from 8 distractor stimuli was presented to monkeys followed by a sequence of single stimuli separated by delay period. We trained animals to identify the salient stimulus on the screen (color and location varied randomly from trial to trial) and to release a lever when another stimulus appeared at the same location. Analysis was conducted on 134 PFC neurons and 71 PPC neurons with significant responses to visual stimuli. We found that the average visual response latency to stimulus arrays was later for PFC neurons (70ms after the stimulus onset) than PPC neurons (50ms) in our experiment. The average time of target discrimination, however, was earlier for PFC neurons (120ms) than PPC neurons (160ms). The results indicate that salient stimuli are represented first in the activity of prefrontal than parietal neurons, although initial latency to the stimulus presentation is shorter for parietal neurons. These findings suggest that prefrontal cortex has a previously unappreciated involvement in the processing of bottom-up factors and plays a role in the guidance of attention to salient stimuli.